1. Field of the Invention
The invention relates to a flocculation apparatus and method for treating colloidal suspensions.
2. Background Description
For improving specific properties of a suspension, for example, the dewaterability or thickenability, a flocculant and/or flocculation auxiliary is conventionally added to the suspension and the latter is worked-up mechanically in a flocculation apparatus. The flocculation itself is carried out in a rapid mixer unit so that flocks form. The flocks are formed in a flocculation apparatus, the resulting flocks being pelleted and rounded by shear forces and flock erosion, so that the desired properties of the flocks, for example, increase in the dewaterability or thickening, can be further improved. However, the shear forces must not be too great because then the flocks are then destroyed and the specific flock properties may deteriorate.
With the rapid mixer, the flocculant and/or flocculation auxiliary is dispersed in a suspension by turbulent flow movements. The formation and adsorption reaction times of the flocculation chemicals are very short, and homogeneous mixing-in of the substances must be ensured for optimizing the flock formation results.
The mixing-in of flocculants and/or flocculation auxiliaries is conventionally effected using stirred vessels or by using tubular reactors with plug flow, such as, for example, injection mixers, inline turbo mixers and pumps. Flock formation using a cylinder stirrer, for example, was investigated by M. Reiter, M. Schmidt and U. Wiesmann: The flow-through cylinder stirrer in the range of turbulent flow—an apparatus with interesting properties, V. T.- Verfahrenstechnik 14 (1980) No. 9, pages 578 to 582. In this investigation, the cylinder stirrer consisted of two coaxial cylinders, of which either the inner or the outer cylinder rotates or both cylinders rotate in the same direction or opposite directions at different speeds. It was found that the optimum energy input number is dependent on the residence time in the cylinder stirrer.
Sludge conditioning using a conical pelleting apparatus was described in A. Hemme, R. Polte, P. Ay: Pelleting flocculation—the alternative to conventional sludge conditioning in Aufbereitungs-Technik 36 (1995) No. 5, pages 226 to 235. The sewage sludge stream runs from the cone base downwards to the cone apex, and the flocculation auxiliary is introduced into the conical gap of the pelleting reactor. In the conical pelleting zone, the flock pellets roll in a circular manner on the pelleting surface. Only the mechanically stable pellets having a certain size and strength are discharged. The conditioning process is controlled by a conical stirrer for generating a circulation flow.
For the optimum conditioning of sewage sludges of varying quality and composition, taking into account other process parameters, it is necessary for the substantial parameters, such as, for example, particle size distribution, porosity or the specific surface area of the sewage sludge, to be reproducibly established.